Process controllers



Sept. 15, 1959 J. w. BUNTING ETAL 2,904,650

PROCESS CONTROLLERS Filed Oct. 23, 1958 MMM United States Patent Ofifice 2,904,650 Patented Sept. 15, 1959 PROCESS CONTROLLERS James William Bunting, Earlsdon, Coventry, and Fred erick Harold Martin, Keresley, Coventry, England, assignors to Courtaulds Limited, London, England, a British company Application October 23, 1958, Serial No. 769,236

Claims priority, application Great Britain October 23, 1957 5 Claims. (Cl. 200-6118) This invention relates to process controllers and in particular is concerned with the detection of movement away from a mean condition and the control of mechanism to restore that condition, such as may be necessary to maintain constant conditions in a great many industrial processes.

For example, in high speed Warp knitting machines, the sheet of warp threads is released from the warp beam at a substantially steady rate corresponding to the rate of operation of the knitting needles so that the beam must be driven at a gradually increasing rate as knitting proceeds to compensate for the decreasing diameter of the warp remaining on the beam otherwise the tension in the threads will rise steadily. The tension in the threads is thus a measure of the relationship between the rate at which yarn is required by the knitting needles and the speed of rotation of the beam, and by leading the threads over a resiliently mounted tension bar between the beam and the needles, the movement of this bar from a mean position can be used to control the beam speed.

The present invention is of particular value wherever the tendency to deviate from a mean value or position needs to be corrected gradually and smoothly, and where it is important that the tendency to over-correct should be reduced to a minimum.

According to this invention a switch for controlling compensating mechanism comprises a member moveable from a mean position in accordance with departures of a variable condition from a fixed value, connected by a lost motion connection to a follower, the movements of which are damped so that the follower remains stationary until moved by the member, and for each direction of departure, contacts which are closed upon the member leaving the mean position, in series with contacts arranged to be closed upon the member reaching the limit of the lost motion in moving away from the mean position, so that a series circuit is completed so long as the member is moving away from the mean position but is open so long as the member is moving towards the mean position. The follow-up member is preferably damped by a friction brake. If the member is in the form of a pivoted arm, the follower should be pivoted on the same axis, and is conveniently driven by the engagement of the arm with adjustable stops on the follower, one on either side of the arm.

A controller according to the invention is shown in the accompanying drawing, in which the variable quantity, such as warp tension to be controlled causes movement of the right hand end of a pivoted arm 1 which is rotatmounted on a base plate 14. An extension 5 of the arm 1 moves between adjustable stops 6 and 7 carried by a follower in the form of a plate 8 which is also rotatable on the shaft 2. The plate 8 is held by stationary friction pads 9, 10, 11, carried on the base plate 14, which bear upon the surface of the plate 8. The plate 8 carries contacts 12, 13, one on each side of the extension 5 of the arm 1. The contacts 3, 4, 12, and 13 are normally open.

The contacts 3 and 13, and the contacts 4 and 12, respectively, are connected in series.

When the arm 1 is moved in a clockwise direction about the shaft 2 from its mean position between the contacts 3 and 4, it closes contacts 3 and the contacts 13 on the plate 8 after which it engages the stop 7 and carries the plate 8 with it. A circuit through contacts 3 and 13 is thus completed which may be employed in any convenient way to restore the variable quantity to its predetermined value, and thus restore the arm 1 to its mean position. As soon as the arm 1 begins to return, leaving the plate 8 for the moment stationary, the contacts 13 open again breaking the circuit before the arm 1 has returned to its mean position and thus preventing overcorrection. As the arm 1 returns, it closes the contact 12 and engages the stop 6, but no circuit is completed through the contact 12 until the arm has passed through the mean position and the contact 4 is closed.

Thus the controller initiates restoring action as soon as the arm 1 makes a predetermined deviation from the mean position, but stops any further increase in the restoring action as soon as the action is sufficiently eifective to cause the arm 1 to move back towards its mean position. Thus over-correction and hunting are avoided.

What we claim is:

l. A switch for controlling compensating mechanism, comprising a member moveable from a mean position in accordance with departures of a variable condition from a fixed value, a damped follower, a lost motion connection between the member and the follower, a first pair of contacts closeable upon the member leaving the mean position in one direction, a second pair of contacts in series with the first pair of contacts and closeable upon the member reaching the limit of the lost motion in moving away from the mean position in that direction, a third pair of contacts closeable upon the member leaving the mean position in a direction opposite to that which closes the first pair of contacts, a fourth pair of contacts in series with the third pair of contacts and closeable upon the member reaching the limit of the lost motion in moving away from the mean position in the direction which closes the third pair of contacts.

2. A switch as claimed in claim 1, in which the mem her and the follower are pivoted on the same axis.

3. A switch as claimed in claim 1, in which the brake on the follower is a friction brake.

4. A switch as claimed in claim 1, in which the lost motion connection comprises adjustable stops on the follower adapted to engage the member.

5. A knitting machine having a warp thread tension control comprising a warp beam let-off drive, a moveable warp thread bar, a switch according to claim 1, and a connection between the switch and the tension bar.

References Cited in the file of this patent UNITED STATES PATENTS WWW UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Now 2,904,650 September 15, 1959 James William. Bunting et e1a It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

0011mm 2, lines 63 to 6'7, strike out the following:

"References cited in the file of this patent UNITED STATES PATENTS 2,582,972 Dungler Jan. 22, 195.2 2,801,308 Cubellis July 30;, 1957" and insert instead No references cited.

Signed and sealed this 5th day of April 1960.

Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Now 2,904,650 September 15, 1959 James William Bunting et al,,

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correct-ion and that the said Letters Patent should read as corrected below.

Column 2, lines 63 to 6'7, strike out the following:

"References cited in the file of this patent UNITED STATES PATENTS 2,582,972 Dungler Jan. 22, 1952' 2,801,308 Cubellis July 30', 1957" and insert instead No references cited Signed and sealed this 5th day of April 1960.

( SEAL) Attest:

KARL Ho AXLINE Attesting Officer ROBERT C. WATSON Commissioner of Patents 

